Well, those were some swift responses! Thank you!
Checked again... I suppose that this statement's what it ultimately comes down to: 'You determine what spells you know and can prepare for each class individually, as if you were a single-classed member of that class.'. This, I assume, is intended to include 'as if you had the spell slots of a single-classed member of that class' but doesn't explicitly spell it out, especially in the light of class spellcasting rules discussing gaining spells 'of a level for which you have spell slots'. Perhaps could be made a touch clearer!
All true! That wasn't really my question, though: I was curious about how people had previously narratively treated what would be constantly dropping and picking up a weapon from a mechanical point of view.
Thank you - and don't worry, I appreciate that! I'm mainly asking for reasons of character development that rely on potential access to 9th Level spells (mainly Wish) far more than actual mechanical attainment of that level of spellcasting. Regardless, I seem to have my answer now!